As is often the case, in those areas where heavy loads must be moved, such as machine shops, auto repair shops, and the like, the employees or workers are in a danger of injuring their backs while lifting or carrying heavy or awkward loads, with subsequent partial or complete incapacitation insofar as their work is concerned. Such back injuries also lead to an inability to perform even normal lifting functions, such as loading luggage into or extracting it from the trunk of a car. Some manner of lifting device, such as a crane, is helpful in all such cases for the person called upon to lift any heavy, or even moderately heavy, articles, to transport them, and to deposit them in a desired location, however, heretofore, most such cranes are too unwieldy for small, mundane tasks.
In general, a crane consists of an elongated boom swivelly mounted on a support structure and movable in azimuth so that the boom may be swung from side to side. The distal end of the boom usually has a pulley or grooved wheel rotatably mounted thereon and over which a lifting cable is passed. The cable itself is paid out from, for example, a drum under control of a winch motor, and the angle of the boom itself relative to the ground generally remains fixed during the lifting operation. For increased versatility and convenience, the boom and associated support structure are often mounted on a mobile platform, which may range from a railroad car to a steerable tricycle arrangement of small wheels. Such mobile cranes as the latter can be used to carry heavy or awkward loads from one place to another, thereby relieving the operator from handling such loads. Typical light weight mobile crane arrangements are shown in U.S. Pat. Nos. 1,840,522 of Mossay and 4,782,962 of Hackworth, et al. Both of these patents disclose cranes which are movable in angular elevation, i.e., the angle of the boom relative to the ground may be adjusted for optimum stability and lifting characteristics. However, the entire structure of the crane has to be moved to change the azimuth direction. In addition, the adjustment of the boom angle, relative to the ground, must be done manually by the operator, which, in the case of a severely handicapped user, can be quite difficult, especially where the boom itself is heavy.
Where the crane or lifting device is to be used for carrying a load from place to place, it is desirable, although not necessary, that the operator be carried by the mobile crane also. To this end, such devices are supplied with a seat for the operator from which he may operate the crane. Examples of such seating arrangements are shown in U.S. Pat. Nos. 2,421,437 of Ryan, et al., 3,926,316 of Luttrell, and 4,763,800 of Engler, et al., in all of which are disclosed seating arrangements for the operator from which he may manipulate the lifting or carrying crane or platform. Of these patents, however, only that of Engler, et al. discloses a motorized or power operated platform and lifting device.
Usually, the mobile type cranes have either a three wheel triangular arrangement as shown in the Mossay patent or a four wheel arrangement as shown in the Luttrell and Hackworth et al. patents, and can be steered by manipulating the wheels, or in the case of Luttrell, by using the feet. In a triangular arrangement, the optimum longitudinal stability is achieved by having the apex of the triangle extend forward under the boom along the longitudinal axis, to prevent the weight at the distal end of the boom from tilting the crane body. However, when the boom, carrying a load, is swung to the side at an angle to the longitudinal axis, the triangular support arrangement can become unstable even to the extent of tipping over. It is known to use laterally extending stabilizer arms to impart stability to the platform and thereby minimize any tendency to tip over. Such arms usually have their distal ends terminating in a flat foot, and, after the load has been lifted, the arms are re-folded up to permit movement of the crane over the ground. Thus, the stability afforded by the arms is lost during transport of the load.
Many cranes, especially the mobile type, are equipped with a counterweight arrangement located on the opposite side of the crane fulcrum from the boom, to compensate for heavy loads carried by the boom. Such counterweights are shown in Mossay, Hackworth et al., and Engler et al. patents. Of particular interest is the arrangement shown by Engler et al. in which the counter weight is made adjustable by the addition or subtraction of weight members. Such an arrangement as shown by Engler et al. requires that the operator lift the weights to place or remove them, which, for handicapped people or people with bad backs, at least to some extent defeats the purpose of a crane designed for use by such people.